Effects of degradation products from gelatin spongy scaffolds on angio-osteogenic capacity

The objective of this study was to determine whether degradation products from spongy gelatin scaffolds can enhance angiogenesis and orthotopic bone regeneration. Spongy gelatin disks were prepared using gelatin solution concentrations ranging from 1% to 7% (v/w) within cylindrical tubes through programmed freezing, lyophilization, cutting, and dehydrothermal crosslinking and implanted in critical-sized defects of rat calvaria for up to 8 weeks. Analyses of disk implantation into rat calvaria defects by microfocus X-ray computed tomography and histomorphometry indicated that the bone volume was significantly larger in the 5% and 7% gelatin sponge groups than in the 1% and 3% gelatin sponge groups and tended to increase progressively from 5% to 7%. The histomorphometric analysis also showed that the largest number of new vessels was formed in the defect treated with 5% gelatin sponge compared to other gelatin sponges. Immunohistochemistry of matrix metalloproteinase (MMP) indicated that the gelatin concentration in the disks affected the appearance of MMP-2 and MMP-9 positive cells around the skeleton of the gelatin sponges. The degradation products of gelatin by MMP-9 and prolyl endopeptidase enhanced the formation of a capillary-like structure in human umbilical vein endothelial cells in vitro. These results suggested that the higher-density gelatin sponges tended to supply their own molecules via biodegradation, resulting in enhanced orthotopic osteogenesis through the expected function of gelatin molecules in angiogenesis and bone formation.